560hp is amazing for a production 3.8L motor. The tuners sill still have plenty of room to work though, just like they do with the Porsche H6. Now whether the new GTR V6 will take upwards of 1000hp on stock internals like the old Nissan RB26DETT remains to be seen. But I am sure we will see 700hp, 800hp, probably even 900hp from the tuners within a year, even if they have to rebuild the motor from the bottom up to get there.

I have heard that Nissan specifically built the engine in a way to make it very difficult for the tuners to extract a lot more power. That being said, FI turners are known to pull off miracles.